Is cancer a death sentence?

far from it. I know many people who had cancer, and lived for a long time after that

Not always.
Some cancers are curable.
Many more can be successfully treated.
Others can be stopped or slowed from progression.

No. Had it twice, two different sorts of cancer, still here. I had surgery, chemo and radiation, extra heavy radiation in a trial.

There are so many various types of cancer, some of which are curable with even minor treatment. So, cancer is not necessarily a death sentence.

Cancer is the second leading cause of death globally, and is responsible for an estimated 9.6 million deaths in 2018. Globally, about 1 in 6 deaths is due to cancer.
Around one third of deaths from cancer are due to the 5 leading behavioral and dietary risks: high body mass index, low fruit and vegetable intake, lack of physical activity, tobacco use, and alcohol use.

Yes it can be a death sentence to many people but not all cancers are death sentences .I have prostate cancer and it hurts sometimes but there are pain killers that can be used to stop this pain .

Not always, depends on the type of Cancer, location of the Cancer and at what stage it's caught.

Pancreatic yes it is. So is brain and so is any late stage diagnosed cancer, regardless of type. 

Pancreatic is a certain death sentence even if early detection. 

yes, you go before the cancer court and if you are convicted with 2 accounts of autism, you will be sentenced to cancer.

There are treatments like chemo that help and can even in a sense cure a person of cancer if the cancer is caught early on. Some people minus treatment with just a very positive mind set managed to beat cancer. We need to put more effort into understanding the brain.